ORGANIC TREE CROPPING
A Big Picture
Although it comes in various forms, organic growing is basically an approach to growing plants with no, or low, chemical input. Purists do it strictly with what they term 'no unnatural input'. Others vary in what is allowed and use things such as copper, lime sulphur and many of the so-called organically-acceptable sprays and concoctions. Under international pressure even commercial growers are trying 'Integrated Fruit Production' and 'Kiwi Green' an endeavour to lower chemical input and also to use what are thought to be less toxic or harmful treatments. Whereas this approach was considered way out some 20 years ago, that is not the aim of so-called 'Official Research Organisations', which is not surprising in view of the extra funding possibilities and overseas marketing requirements. Our new coalition government has announced an increase of some $30 million for organic research.
To understand why there is more interest in organic methods, we should consider how mankind has been spoiling this planet. Consider the over-grazing, the deforestation and the soil-destroying cropping in the Middle East and Europe over the previous centuries. Advances in scientific knowledge have dominated the last 100 years, and continue to accelerate. We now have the capacity to do enormous good to planet earth or enormous harm. Caring for our world is becoming a necessity, not a luxury; and our children's children will bless us or curse us according to the outcome.
That is the big picture. Generally, however, we work on an individual small scale, and play our part on our section, orchard or farm. The decision becomes, "how will we leave it?" This choice, to use organic principles, can often be easier for lifestyle properties than for truly commercial enterprises where the current income depends on this year's crop. Nevertheless, expertise and interest in the organic approach to horticulture and forestry is increasing throughout Europe, America and New Zealand, and the concept should be taken seriously.
But, although we theorise otherwise, in the organic approach we are still bending nature to our own purposes, and this will cause some conflict one way or another. Organic methods do not eliminate pests and diseases, they only manage them at acceptable levels. Our natural greed must be replaced by a little give and take. The desirable level of pest management requires both a living, healthy soil, full of worms and bacterial activity, and the local buildup of insect predators.
There are three basic things we must consider if we wish to improve our environment:
- • The soil;
- • The environment above the soil;
- • The genetic makeup of the trees we choose to grow.
The soil
All soil can be improved by incorporating organic matter. This is one of the basic tenets of organic growing. Sandy soil is given more body and clay becomes more friable. Soil health and life improve because worms love organic matter, fungi and bacteria multiply and the soil becomes alive. Moisture penetration and retention improve, and roots can explore the soil more thoroughly.
Green manure crops
These are one means of building up the organic content and nutrient status of the soil.
They are usually grown quickly and then cultivated in. The types of plants used are legumes (lupins, peas, broadbeans), cereals (oats, barley) and annual grasses. Green crops provide better soil protection while the crop is growing. When tilled in they improve the nutrient status of the soil and provide more humus. As a result there is improved soil structure, and a better habitat for natural predators is created.
Mulches
Surface applications of mulches can also benefit the soil environment by:
- • protecting the soil from the impact of rain;
- • evening out temperature fluctuations;
- • protecting the soil from wind erosion;
- • preventing the soil drying out;
- • making weed control easier;
- • protecting roots which are close the surface.
Mulches gradually become incorporated into the soil through worm and microbial action. In fact, if you observe what happens in the forest, this is the natural progression.
Permanent lays
These can be the usual grass/clover mix, but include extra herbs, flowering plants and deep-rooted weeds if you want to encourage the natural predators of insect pests. Any undesirable weeds can be controlled by cultivation (or other means) before serious planting takes place.
The environment
Woodlands provide a model for a healthy environment. In horticulture we can modify the environment by the spacing of shelter trees, the orientation, pruning and type of trees planted, water (drainage or irrigation), ground cover or lack of it (pasture lays or mulches), monocultural or companion planting. Artificial modification can be achieved by protection from hail, birds or vermin, building shadehouses and glasshouses, and by providing ridges and training systems. All these modifications can affect the presence or absence of insects, disease, animals and birds, the temperature range, the freshness of the air, its humidity and the amount of sunlight. Many or all of these are interrelated, which leads to the philosophy that organics deals with the environment. Healthy soil and a healthy environment should ensure that the plants to be grown are also healthy.
| Insect predators | Beneficial habitats |
|---|---|
| spiders | cocksfoot, tansy, buckwheat |
| beetles | cocksfoot |
| hover flies | tansy leaf, green manure, flowers |
| parasite wasps | buckwheat, Umbelliferae flowers |
| Encarsia enforca | warm sheltered site + white fly |
| ladybirds | mixed pastures and shrubberies |
| praying mantis | mixed pastures and shrubberies |
| lacewings | mixed pastures and shrubberies |
|
21 additional
parasitoids of leaf-roller birds (waxeye, etc) predator mites | bush mite host plants |
We do not fully understand the habitats of all the natural predators but some principles have become evident. Flowering pastures and mixed shrubberies and shelters supply attractive habitats for predators while closely-cut swards do not. Our treatment of the soil should encourage the total health of plants and animal life, insects and microflora, and probably a myriad of other things we don't understand. A truly organic system probably needs the input of animals or birds to improve the nutrient cycle.
The genetic influence
The genetic makeup of the trees we put on our property can have a major influence on how healthy and fruitful they are. Any obvious disease or pest problems should be tackled, sick trees removed and burnt, and drainage improved if there are root problems. Improve the habitats for the predators you need, even bring some in if they are not present. Select rootstocks to suit your conditions, from healthy, virus-free material. When choosing your species and varieties, again choose only healthy specimens, resistant to, or at least tolerant of, diseases, with not too many of the same thing together. Get varieties suited to your district. Tree Croppers in your area should be able to help with local knowledge. Avoid obvious problem trees.
Organic kiwifruit
The kiwifruit industry has taken a step in the right direction with "Kiwi Green"; overseas visitors were often horrified by the chemicals we previously used. It makes commercial common sense to think organically, because overseas markets are heading in that direction. And the European and Japanese markets are short of suitable fruit, now that the housewives have become aware of organic products. Traditional values of simplicity and natural flavours are coming back.
A number of organic methods can be used by kiwifruit growers. Instead of bare strips, use grass or clover permanent swards under the vines. If sheep are used to keep them under control, mowing may be needed only twice a year. An open canopy will allow plenty of sunlight and fresh air movement around the vines. This adds flavour to the fruit and reduces the risk of fungus diseases. Use foliar seaweed sprays and BT (Bacillus thuringiensis) for leaf-roller and scale. If organic compost is to replace artificial fertilisers, than start by applying about 10 tonnes/ha, lowering this to 2t/ha for maintenance. Biodynamic preparations are used by some people. Cleanliness is important, achieved by washing tractors and cleaning up rubbish.
Organic apples
Again, markets in the USA are keen for this product from New Zealand, and the markets are large. Some supermarkets in New Zealand are now stocking organic produce. Half of growers asked to comment are interested in trying organic production methods. 'Integrated Fruit Production' has been introduced to all apple growers as a system to lower chemical input and use less toxic material. When to spray is decided by an orchard assessment of the problems.
Black spot (scab) (Venturia inaequalis) is the major problem for organic production and can ruin the whole crop. Control is achieved' by sprays of copper and sulphur, and early and late sprays of lime sulphur. Baking soda and lime are also used. There are also some resistant varieties. Black spot over-winters on leaf litter, which is broken down completely with organic swards, whereas the leaves are still there in spring when herbicides are used.
Powdery mildew (Podosphaera leucotricha) is a problem for the tree, but does not destroy the fruit, so you may be able to live with it. However, controls used are seaweed foliar sprays, baking' soda, lime, and also vegetable oils. there are resistant varieties here, too.
Pests, such as leaf-roller and codling moth, can be controlled by using corrugated cardboard bands around the trunk, sex pheromones (best in large orchards), granulosis virus (8-9 sprays), and BT sprays.
Woolly apple aphid is controlled by using resistant rootstocks. In New Zealand, insects resistant to insecticide include leaf-roller, mealybug, and leaf-hoppers. Insecticide-resistant codling moth exists in the USA and South Africa.
Other crops
Many fruit crops (blueberries, persimmons, feijoas, pears, nashi, plums and avocados) can be grown reasonably easily without sprays. Usually, diseases will be contained by their natural resistance or your good husbandry. This doesn't mean they will be insect-free so, while they are suitable for the local market and your own use, they are unacceptable for export. Export fruit would need some post-harvest (or pre-harvest) treatment to remove undesirable insects.
As far as stonefruit are concerned, you need varieties resistant to curly leaf and brown rot to overcome these major problems. Black spot would be a problem with European pears but some varieties are resistant.
Nut production doesn't really allow you to have flowers growing right through the orchard, because nuts are harvested from the ground. These crops will need to sort out their own organic systems. Again, copper, sulphur and lime sulphur will control the fungal problems, and natural resistance is present in some varieties.
Conclusion
Organics is an ideal to work toward. It is still a managed system when operating correctly
and there are many gaps yet in our knowledge of how to grow crops organically. However, it does offer all of us a healthier alternative to chemical residues in our food chain, not to mention providing healthier and more pleasant conditions for ourselves and our staff to work in. Also, our overseas customers are beginning to demand it.
Our grandfathers used many of these new/old methods: animal manures, seaweed, compost, and organic matter in the soil. Fruit production is more difficult than the old mixed cropping/animal farm that really was an organic system. Our modem monocultural specialisation makes a truly organic way difficult to achieve. It will be easier on a mixed lifestyle block.
Changing to organics takes time. Three years is often mentioned for the transition to allow beneficial insects to build up. This may mean two rough years or some form of overlap. Again, this is difficult for truly commercial people, but Kiwi Green and Integrated Fruit Production systems seem to be a good move in the right direction for apples and kiwifruit.
DATE: August 1997
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